This invention relates to a process for treating an image-forming laminated plate. In other words, this invention relates to a process for effecting an image formation on the same laminated plate which comprises a base substrate, a photosensitive layer containing a substance with quinonediazide structure and a silicone rubber layer.
Various types of the image-forming laminated plate are well known. Among others, a variety of proposals have been offered to a dry planographic printing plate which is provided with a silicone rubber layer on a photosensitive layer superimposed on a base substrate.
For instance, with respect to a positive working printing plate, U.S. Pat. No. 3,677,178 discloses a planographic printing unprocessed plate laminated with a silicone rubber layer on a photohardening diazo-sensitized layer overlying on an aluminum substrate, and proposes that the unprocessed plate is exposed through a positive transparency and then both the soluble diazo-sensitized layer and the silicone rubber layer in the unexposed areas are washed off with a developer to lay bare the surface of the aluminum substrate as image area.
U.S. Pat. No. 3,894,873 discloses a planographic printing unprocessed plate laminated with a silicone rubber layer on a photoadhesive layer superimposed on a base substrate, and proposes to expose the unprocessed plate through a positive transparency. According to U.S. Pat. No. 3,894,873, the photoadhesive layer in the exposed areas is polymerized and adheres firmly to the silicone rubber layer overlying thereon while the photoadhesive layer in the unexposed areas remains unchanged and retains its original weak adhesion to the silicone rubber layer. Then, by developing with a developer, only the silicone rubber layer in the unexposed areas is removed without difficulty and the underlying oleophilic photoadhesive layer is laid bare, and on the other hand, the silicone rubber layer in the exposed areas is remained on the underlying exposed photoadhesive layer. The bared surface of the oleophilic photoadhesive layer becomes an ink-receptive area or image area and the still remained silicone rubber layer becomes an ink-repellent area or non-image area.
With respect to a negative working printing plate, U.S. Pat. No. 3,511,178 discloses a planographic printing unprocessed plate provided with a silicone rubber layer through an adhesive layer on a photosoluble diazo-sensitized layer superimposed on an aluminum substrate, and proposes that the unprocessed plate is exposed through a negative transparency and the photosensitive layer in the exposed areas is dissolved and removed by a developer simultaneously together with the silicone rubber layer overlying thereon to lay bare the surface of the aluminum substrate as image area.
Further, UK Patent Applications GB No. 2064803A and GB No. 2034911A disclose a planographic printing unprocessed plate comprising a base substrate, a photosensitive layer of photodecomposable type and a silicone rubber layer in a superimposed relation, and propose that the unprocessed plate is exposed through a negative transparency and the silicone rubber layer, as occasion demands, together with the underlying photosensitive layer in the exposed areas is removed by a developer to lay bare the surface of the photosensitive layer or the base substrate as image area.
In the above-mentioned treatment of the image-forming laminated plate, i.e., the treatment for converting the image-forming laminated plate into the printing plate, the adhesion between the photosensitive layer and the silicone rubber layer overlying thereon is a extremely important factor for formation of definite image on the printing plate. The merely strong adhesion therebetween is, however, not sufficient but it is more important to create a large difference between the adhesion of the photosensitive layer to the overlying silicone rubber layer in the exposed areas and that in the unexposed areas.
In addition, the swelling property and solubility of the photosensitive layer in a developer are likewise improtant factors for the same purpose. The merely high solubility and favorable swelling property alone are not sufficient, but it is important as well to create further a large difference of the solubility and swelling property of the photosensitive layer in the exposed areas from those in unexposed areas.
The prior arts have offered several propositions from the foregoing view points. For instance, according to U.S. Pat. No. 3,677,178 the photosensitive layer in the exposed areas is made insoluble into the developer by photo-crosslinking of the diazo group, according to U.S. Pat. No. 3,894,873 the adhesion between the photoadhesive layer and the silicone rubber layer in the exposed areas is made firm by photo-polymerizing the photoadhesive layer, according to U.S. Pat. No. 3,511,178 the diazo photosensitive layer becomes soluble in the developer as a result of exposure, according to GB No. 2034911A the quinonediazide photosensitive layer is made soluble in the developer by the exposure and moreover according to GB No. 2064803A the strength of the adhesion between the photosensitive layer and the silicone rubber layer is reduced by the exposure and the silicone rubber layer in the exposed areas is removed by a development.
As described hereinbefore, in the image-forming laminated plate so far proposed including the cited references, a direct change in the adhesion or the solvent resistance of the photosensitive layer has been caused by the actinic light, for instance, the enhancement or inversely reduction of the adhesive strength between the silicone rubber layer and the photosensitive layer by the exposure and the solubilization or inversely insolubilization of the photosensitive layer in the developer by the exposure. However, according to the conventional treatment for effecting the image formation, neither the difference of the adhesion of the photosensitive layer to the silicone rubber layer between the exposed and unexposed areas nor the difference of the solubility and swelling property of the photosensitive layer between the exposed and unexposed areas is expected to be large enough. Consequently, there are observed some drawbacks of unsatisfactory results. That is, upon the minute alternation of the developing conditions, the areas to be remained on the plate surface, which areas are corresponding to the silicone rubber layer forming the non-image background in the dry planographic printing plate having the upper layer of silicone rubber, may be wholly or partially removed therefrom, leading to the defect in the non-image area. On the other hand, similarly upon the minute alternation of the developing conditions, the areas to be removed from the plate surface, which areas are corresponding to the silicone rubber layer superimposed on the photosensitive layer to be formed into the image area in the dry planographic printing plate having the upper layer of silicone rubber, may be wholly or partially remained thereon, leading to the difficulty or inferiority of development. In such a manner, since either the wholly or partially removal of the non-image area or the difficulty and inferiority of development is caused by the minute alternation of developing conditions, the latitude which allows the formation of definite image, i.e., the latitude of development is very narrow and it is difficult to obtain a sharp image formation.
Furthermore, in the conventional treatment, the image formation largely depends on the temperature and humidity during the development. For instance, even in the practical range of temperature and humidity, the relatively high temperature or relatively high humidity causes the removal of the non-image area and the relatively low temperature or relatively low humidity causes the inferiority of development.
The developing time also has influence on the image formation. For instance, by the long time rubbing with a developing pad or the long time immersion into the developer, a part of the laminated photosensitive and silicone rubber layers in the non-image area, both of which should firmly adhere to each other to form the printing plate, is occasionally removed due to the damage of adhesion therebetween by the developer, or the photosensitive layer to be remained in the image area is occasionally removed during the development due to the swelling and dissolving thereof by the developer. Thus, there can be observed the difference of the image formation between the long time development and the short time development.
Still more, the conventional image formation also largely depends on the rubbing condition during the development, for instance, the load added thereto during rubbing with the developing pad and the number of rubbing. The strong rubbing which means the high load or the large number of rubbing causes the damage of adhesion to remove the non-image area, while the weak rubbing which means the low load or the small number of rubbing causes the poor reproducibility of the image to make the reproducibility of small halftone dots difficult. Thus, the latitude in image reproducibility is narrow.
In addition to the above-mentioned, there are other defects in the treatment hitherto proposed, for instance, the spoiled image fidelity due to the generation of gaseous nitrogen from the photosensitive layer of quinonediazide during the exposure and the retainment of photosensitivity in the developed plate due to the incomplete desensitization leading to the fear of damaging the printing plate in the step of washing the plate surface on the printing machine.
As hereinbefore described, the disadvantages confronted at present in the image formation are the extreme narrowness of latitude in the image reproducibility, the poor solvent resistance and the unfavorable developing speed in the conventional treatment of the image-forming laminated plate, particularly the dry planographic printing unprocessed plate having the photosensitive layer and the silicone rubber layer. These disadvantages are mainly originated in the adhesion between the superimposed layers, especially in the small difference of adhesion between the exposed area and the unexposed area.
The object of the present invention is to obtain a sharp image formation, of which image boundaries are precisely defined, on the image-forming laminated plate, especially the dry planographic printing unprocessed plate.
Another object of the invention is to create a large difference of adhesion of the photosensitive layer to the silicone rubber layer between the image area and the non-image area.
The further object of the invention is to create a large difference of the solvent resistance of the photosensitive layer between the image area and the non-image area.
Moreover, the object of this invention is to enlarge the latitude in the image formation or the latitude of development.
The other objects of the present invention will be apparent from the descriptions hereinafter.